My JD 650 suddenly had the tachometer fail. Not that you really need it, but the hour meter was frozen and I keep track of that for maintenance purposes. I obtained a replacement from JD, had no problem replacing the cable but discovered the cause of the problem was the meter itself. The cable broke at the takeoff for the motor, but the meter would no longer turn. I thought about disassembly as I have watch repair experience, but it looked like no obvious way to get at the insides. The glass appeared to be glued on. My solution was to let it set with JD penetrating oil, crank the meter by hand with vice grips attached to the new cable. I oiled it and it now works fine. Questions from me, how does one remove the glass from the meter and should the meter need attention again is it possible to clean the unit or is it permanently sealed? Thanks. We are now back to cutting with my favorite tractor, 24 years old and still going strong!